Effects of estradiol on proliferation of LF cells by MTT assay. Proliferation of ligamentum flavum cells was measured by MTT assay at 24 hours (A), Day 3 (B) and Day 7 (C) treated with 17β-estradiol (10-7 >M, 10-8 M, 10-9 M, and 10-10 M). The level of proliferation was presented as optical density (O.D.) of absorbance at 570 nm. (n = 6; * p <0.05).